Breast cancer is the third most common cancer, and the most common cancer in women, as well as a cause of disability, psychological trauma, and economic loss. Breast cancer is the second most common cause of cancer death in women in the United States, in particular for women between the ages of 15 and 54, and the leading cause of cancer-related death (Forbes, Seminars in Oncology, vol. 24(1), Suppl 1, 1997: pp.S1-20-S1-35). Indirect effects of the disease also contribute to the mortality from breast cancer including consequences of advanced disease, such as metastases to the bone or brain. Complications arising from bone marrow suppression, radiation fibrosis and neutropenic sepsis, collateral effects from therapeutic interventions, such as surgery, radiation, chemotherapy, or bone marrow transplantation-also contribute to the morbidity and mortality from this disease.
While the pathogenesis of breast cancer is unclear, transformation of normal breast epithelium to a malignant phenotype may be the result of genetic factors, especially in women under thirty (Miki, et al., Science, 266: 66-71 (1994)). However, it is likely that other, non-genetic factors also have a significant effect on the etiology of the disease. Regardless of its origin, breast cancer morbidity increases significantly if it is not detected early in its progression. Thus, considerable efforts have focused on the elucidation of early cellular events surrounding transformation in breast tissue. Such efforts have led to the identification of several potential breast cancer markers. For example, alleles of the BRCA1 and BRCA2 genes have been linked to hereditary and early-onset breast cancer (Wooster, et al., Science, 265: 2088-2090 (1994)). However, BRCA1 is limited as a cancer marker because BRCA1 mutations fail to account for the majority of breast cancers (Ford, et al., British J. Cancer, 72: 805-812 (1995)). Similarly, the BRCA2 gene, which has been linked to forms of hereditary breast cancer, accounts for only a small portion of total breast cancer cases.